A 4 November SEC notice sets out an IEX rule amendment intended to clarify when US equity trading can resume after the most severe market-wide circuit-breaker event. The filing, SR-IEX-2026-45, responds to other national exchanges preparing longer, near-overnight trading schedules. It is a market-continuity rule, not an announcement that such a market crash occurred.[1]
A Level 3 market-wide circuit breaker is associated with a 20% fall in the S&P 500 against the previous day’s closing level and ends trading for the remainder of the applicable trading day. When some venues operate a session that crosses conventional calendar boundaries, the meaning of the next session becomes operationally important.[1]
The IEX proposal addresses resumption of trading after that severe halt so that overnight session definitions do not allow an unintended restart during the same shutdown. It is especially relevant for a broker routing to more than one venue: if one exchange’s calendar labels differ from another’s, a unified risk and order-state policy is still necessary.[1]
Market-structure boundaries
| Measure or condition | Verified scope |
|---|---|
| SEC notice | Release 34-106810; 4 November 2026 |
| Exchange filing | SR-IEX-2026-45 |
| Relevant shock | Level 3 market-wide circuit breaker; 20% S&P 500 drop |
| Reason for clarification | Other venues planning expanded overnight equity sessions |
| Not announced | A Level 3 event or a new IEX 23-hour trading launch |
IEX itself is not represented in the notice as already running a 23-hour trading programme. The filing explicitly discusses other exchanges’ upcoming expansion and corresponding changes needed in its rulebook. Announcing a harmonisation rule therefore should not be mistaken for an IEX launch of an around-the-clock cash equities venue.[1]
For risk teams, the critical implementation work includes consistent handling of open orders, market-data status, routing disablement, customer notifications and the reopening condition. A market-wide halt is different from a single-stock volatility pause; treating them interchangeably can lead to unfilled or incorrectly routed orders at stressed moments.[1]
The SEC notice describes a filing designated for immediate effectiveness while soliciting public comments. That procedural label does not mean a future market-wide halt has been tested in production, nor that the planned 23-hour schedule has already gone live at every venue. The document supplies the rule intent and filing status; actual operating calendars remain venue-specific.[1]
Sources & further reading
- IEX proposed change to Level 3 market-wide circuit-breaker resumption rule, 34-106810 US Securities and Exchange Commission · 4 Nov 2026 · Accessed 5 Nov 2026